In addition to intermittent, reversible obstruction, some asthmatics, develop fixed airway obstruction known as remodeling. A growing literature suggests thatTGFpt produced by activated and long-lived airway and parenchymal eosinophils (EOS) induces hyperplasia of bronchiolar fibroblasts, smooth muscle and myoepithelial cells culminating with enhanced production of collagens and extracellular matrix proteins. Remodeling is reduced when eosinophils are eliminated from the airways suggesting that suppression of EOS derived TGFpl or blockade of its profibrotic signaling in cellular targets could have therapeutic benefits. Recently, we have identified Pin1, a peptidyl-prolyl isomerase (PPIase) as a participant in TGF(31 production and signaling. Pin1 is related to cyclophilin A and FKBP and is the only known eukaryotic enzyme that binds to and catalyzes the cis-trans isomerization of phosphoserine-proline or phosphothreonine-proline peptide bonds. The isomerization of target proteins alters their conformation, function or stability. Pin1 has recently been implicated in GM-CSF mRNA metabolism, suggesting a broader role in the regulation of cytokine biogenesis by activated EOS. We now present evidence that Pin1 regulates TGFpl expression by EOS and TGFpl signaling in fibroblasts. Specific blockade of PinVs PPIase activity in EOS reduced TGFpl mRNA stability, causing steady state mRNA levels and protein expression to significantly decline. Immunoprecipitation studies revealed that Pint binds to multiple proteins that have been implicated in the regulation of TGFpl mRNA decay or gene expression. Pin1 inhibition reduced collagen mRNA accumulation in bronchial airway derived fibroblasts exposed to TGFpl in vitro as well as in the airways, bronchoalveolar lavage (BAL) cells and lung parenchyma of allergic rat models of asthma treated in vivo. Therefore, we hypothesize that Pin1 is a critical, signaling intermediate that plays a key role in the production and action of TGFpl in the asthmatic lung. We therefore propose to: 1. Identify how Pin1 isomerase activity is regulated after eosinophil activation, 2. Determine how Pin1 protein targets HuR and AUF1 control TGFpl mRNA decay, 3. Determine how Pin1 regulates TGFpl signaling in fibroblasts and 4, Determine if Pin1 blockade can alter airway remodeling in animal models of chronic allergen exposure. In aggregate these studies will clarify the role and function of Pin1 in asthma pathogenesis and airway remodeling.